Foster F40 - Manual (Page 10)

COMPRESSOR, WATER INLET SOLENOID VALVE, HOT GAS VALVE
NOTE: The length of the defrost cycle is (non-adjustable) automatically determined by the microprocessor of The P.C. BOARD in relation to
the time T2 necessary for the unit to reduce the evaporator temperature from 0˚C (35˚F) to -1 3˚C (8.5˚F) and of the ambient temperature, as
illustrated in Table C.
As shown it is possible to have a different length of the defrost cycle in connection with the different length of the second phase of the freezing
cycle T2 relative to the ambient temperature situations; shorter when the ambient temperature is high and longer in colder ambients so to
partially compensate the length of the freezing cycle, which is longer in high ambient temperatures and shorter in low ones.
H. Check, during the defrost cycle, that the incoming water flows correctly into the sump reservoir in order to refill it and that its surplus overflows
through the overflow drain tube.
I. Check the texture of ice cubes just released. They have to be the right shape with a small depression of about 5-6mm in their crown.
If not, wait for the completion of the second cycle before performing any adjustment.
If the ice cubes require a correction to their shape, it is possible to modity the length of the timed freezing cycle by changing the DIP SWITCH
keys setting as illustrated in table B.
It the ice cubes are shallow and cloudy, it is possible that the ice maker runs short of water during the freezing cycle second phase or, the quality
of the supplied water requires the use of an appropriate water filter or conditioner or the installation of the optional water drain valve kit KWD.
J. To be sure of the correct operation of the ice level temperature sensor, located in one side of storage bin liner, during the defrost cycle place
one shovel of ice cubes in contact with its probe for approx. 30 sec.-1 minute.
As the temperature of storage bin sensor reaches the value of +2˚C (35˚F), the ice level control transmits a signal to the microprocessor of the
P.C. BOARD in order to stop the ice maker operation at the end of the defrost cycle with the simultaneous glowing of the 3rd RED LIGHT, to
monitor the BIN FULL situation (Fig.6). Page 13
With no more ice cubes in touch with the ice level control the temperature of its probe progressively rises to reach + 4.5˚C (40˚F) and at this
point the ice machine restarts to initiate a new freezing cycle with the simultaneous extinguishing of the 3rd RED LIGHT.
NOTE The CUT-IN RANGE OF THE ICE LEVEL CONTROL SENSOR can be adjusted as shown in table D; its cut out setting remains however
at + 2˚C (35˚F).
6. Principle of Operation
6.1 How it works
In the cube ice makers the water used to make the ice is kept constantly in circulation by an electric water pump which primes it to the spray
system nozzles from where it is diverted into the inverted mould cups of the evaporator. A small quantity of the sprayed water freezes into ice;
the rest of it cascades by gravity into the sump assembly below for recirculation.
6.2 Freezing Cycle
The hot gas refrigerant discharged out from the compressor reaches the condenser where, being cooled down, condenses into liquid. Flowing
into the liquid line it passes through the drier filter, then it goes all the way through the capillary tube where, due to the heat exchanging action,
it loses some of its heat content so that its pressure and temperature are lowered as well.
Next the refrigerant enters into the evaporator serpentine (which has a larger l.D. than the capillary) and starts to boil off; this reaction is
emphasised by the heat transferred by the sprayed water.
The refrigerant then increases in volume and changes entirely into vapour.
The vapour refrigerant then passes through the suction accumulator (used to prevent any small amount of liquid refrigerant reaching the
compressor) and through the suction line. In both the accumulator and the suction line it exchanges heat with the refrigerant flowing into the
capillary tube (warmer), before being sucked into the compressor and recirculated as hot compressed refrigerant gas.
The freezing cycle is controlled by the evaporator temperature sensor (which has its probe in contact with the evaporator serpentine) which
determines the length of the first and second portion of it and it is signalled by the glowing of the 6th RED LED.
The first portion length or time T1 (non-adjustable) is equal to the time required by the temperature sensor to fall to 0˚C (35˚F). When reached,
it is signalled by the glowing of the 5th RED LED.
NOTE If, after 15 minutes, the evaporator temperature has not yet reached the value of 0˚C (35˚F) (due to a partially or total shortage of
refrigerant or to a too high condensing temperature, etc.) the sensor, through the P.C. BOARD, causes the unit to stop the operation with the
simultaneous glowing of the SECOND RED WARNING LED (Fig. 7). Page 13. After having eliminated the source of the unit trip off, to restart
the machine operation it is necessary first to rotate the program selector to the RE-SET position, then put it again on to OPERATION position
or, alternatively, switch OFF and ON the unit at the power line Main Switch.
The second portion length of freezing cycle or time T2 (non-adjustable) is equal to the time required by the evaporator temperature to go from
0˚C (35˚F) to -13˚C (8.5˚F) on models 20, 30, 40 and 60 or to -16˚C (3˚F) on model 85. The sensor will light-up the 4th RED LED.
NOTE In case the time T2 gets longer than 45 minutes, the unit stops with the glowing of the second RED WARNING LED.
Also in this case, after having eliminated the source of the trip OFF to restart the machine it is necessary first to rotate the program selector to
the RESET position then put it again on OPERATION or, switch OFF and ON the unit at power line Main Switch.
The third portion or time Ta (added time) of the freezing cycle is controlled by the electronic timer of P.C. BOARD. As the evaporator temperature
reaches the value of -13˚C (8.5˚F) or to -16˚C (3˚F); the sensing probe of the evaporator sensor (in contact with the serpentine) changes its
electrical resistance causing a low voltage current to flow to the P.C. BOARD which, thereby, activates an electronic timer.
NOTE The activation of the timer (Time mode) of P.C. BOARD is signalled by the glowing of fourth RED LED located in the front of the P.C.
BOARD.
ATTENTION In case the length of the second portion of freezing cycle or time T2, lasts as long as between 35 and 45 minutes, the
third portion or time Ta gets skipped by the P.C BOARD which puts the unit directly in the defrost or harvest cycle.
The length of the third portion of the freezing cycle (adjustable) is pre-fixed and related to the setting of the DIP SWITCH keys 3, 4, 5, 6 and
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11. Principle of Operation
11.1 How it works
In the cube ice makers the water used to make the ice is kept constantly in circulation by an electric water pump which primes it to the spray
system nozzles from where it is diverted into the inverted mould cups of the evaporator. A small quantity of the sprayed water freezes into ice;
the rest of it cascades by gravity into the sump assembly below for recirculation.
11.2 Freezing Cycle
The Hot refrigerant gas discharged out from the compressor reaches the condenser where, being cooled down, condenses into liquid. Flowing
into the liquid line it passes through the drier filter, then it goes all the way through the capillary tube where, due to the heat exchanging action,
it loses some of its heat content so that its pressure and temperature are lowered as well.
Next the refrigerant enters into the evaporator serpentine (which has a larger I.D. then the capillary) and starts to boil off; this reaction is
emphasized by the heat transferred by the sprayed water.
The refrigerant then increases in volume and changes entirely into vapour.
The refrigerant vapour then passes through the suction accumulator (used to prevent any small amount of liquid refrigerant from reaching the
compressor) and through the suction line. In both the accumulator and the suction line it exchanges heat with the refrigerant flowing into the
capillary tube (warmer), before being sucked in the compressor and to be recirculated as high pressure, high temperature gas.
The freezing cycle is controlled by the evaporator temperature sensor (which has its probe in contact with the evaporator serpentine) that
determines the length of the cycle first portion.
When the temperature of the evaporator serpentine drops to a pre-set value, the evaporator sensor probe changes its electrical resistance
allowing a low voltage current (8-10 volts) to flow to the P.C. BOARD which in turn activates an electronic timer.
The timer, which is built-in the P.C. BOARD, takes over, from the evaporator temperature sensor, the control of the freezing cycle up to its
completion.
NOTE: The change of the electrical potential of the evaporator sensor with the consequent activation of the timer (Time mode) is signalled by
the glowing-up of the RED LED located in the front of the P.C. BOARD.
ATTENTION: In case, after 15 minutes from the beginning of the freezing cycle, the temperature of the evaporator sensor probe is higher then
0°C (32°F) (Shortage of refrigerant, inoperative hot gas valve, etc.) the P.C. BOARD switch OFF immediately the unit with the simultaneous
blinking of the WARNING RED LED.
The length of the second portion of the freezing cycle is pre-fixed and related to the setting of the first four DIP SWITCH keys which is made in
relation with the different unit versions.
The DIP SWITCH keys setting is made in consideration of the type of condenser used.
In Table B, page 18, are indicated the various lengths of the second portion of freezing cycle (Time mode) in relation to the different combinations
of the DIP SWITCH KEYS.
In Table A, page 18, is illustrated the DIP SWITCH keys combinations for the different unit versions as they are set in the factory.
The electrical components in operation during the freezing cycle are:
COMPRESSOR
FAN MOTOR (in air cooled version)
WATER PUMP
CONTACTOR COIL
and during the second phase of freezing cycle (Time mode) they are joined by the
ELECTRONIC TIMER
The refrigerant head pressure, in the course of the freezing cycle, ranges between 13.5 and 14.5 bars (190-205 psig) being controlled by the
temperature sensor probe located within the condenser fins (Air cooled version) or, it is kept constant at 14 bars (195 psig) by means of the
water regulating valve (water cooled version).
On the air cooled version, the condenser temperature sensor, when senses a rising of the condenser temperature beyond the pre-fixed limit,
changes its electrical resistance and send a low voltage power signal to the Micro Processor of P.C. BOARD which in turn energizes, through
a TRIAC, the FAN MOTOR.
When the opposite situation occurs, i.e. the condenser temperature gets below the pre-fixed limit, the temperature sensor changes again its
electrical resistance reducing therefore the current flow to the P.C. BOARD to cause the fan motor to temporary cut-off.
NOTE: In case the condensor temperature probe senses that the condensor temperature has rised to 70°C (160°F) - on air cooled versions
- or 62°C (145°F) - on water cooled versions - for one of the following abnormal reasons:
CLOGGED CONDENSOR (Air cooled version)
FAN MOTOR OUT OF OPERATION (Air cooled version)
INSUFFICIENT FLOW OF COOLING WATER (Water cooled version)
AMBIENT TEMPERATURE HIGHER THEN 40°C (100°F)
it causes the total and immediate SHUT-OFF of the machine in order to prevent the unit from operating in abnormal and dangerous conditions.
When the ice maker stops on account of this protective device, there is a simultaneous glowing of the RED LED, warning the user of the Hi
Temperature situation. After having eliminated the source of the condensor hi-temperature, to restart the machine it is necessary first, to rotate
for a while the program selector on RE-SET position then, to rotate it again on OPERATION position.
The same can be done by just switching OFF and ON the unit at main line switch.
The ice machcine resumes its normal operation by going through the 5 minutes water filling phase.
At the start of the freezing cycle the refrigerant suction or lo-pressure lowers rapidly to 3.3 bar-45 psig then it declines gradually - in relation
with the growing of the ice thickness - to reach, at the end of the cycle, approx. 1 bar -14 psig with the cubes fully formed in the cup moulds.
The total length of the freezing cycle ranges from 15-18 minutes.
11.3 Defrost or Harvest Cycle
As the electronic timer has carried the system throughout the second phase of freezing cycle, the defrost cycle starts.
ATTENTION: In case the unit is be able to reach 0°C (32°F) evaporating temperature within 15 minutes, or after 45 minutes from the beginning
of the freezing cycle it has not yet reached the evaporator temperature of -15°C (5°F), the machine goes straight into the defrost cycle omitting
the timed portion of the freezing cycle related to the setting of the first four DIP SWITCHES.
NOTE: The length of the defrost cycle is pre-determined by the setting of the DIP SWITCH KEYS NO. 5, 6 and 7 and it is related as well to the
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